1. Field of the Invention
The present invention generally relates to a lens. More particularly, the present invention relates to a lens for chromatic aberration compensation.
2. Description of Related Art
In recent years, a variety of optical electronic device have been developed, wherein the lens is a major and an important optical components. The lens may be used in, for example, the brightness enhancement layer of the backlight module of the display panel of mobile phone, or camera, or in the optical pickup head of CD-ROM, VCD-ROM, or DVD-ROM. Especially, lens is an important component of digital still camera (DSC) and digital video camera (DVC). The reliability of the optical products is considerably dependent on the processing of the light source via the lens. Conventionally, if white light is used as the light source of the optical products, generally the aberration is generated.
FIG. 1A is a drawing schematically illustrating the aberration generated by a conventional white light via a lens. Referring to FIG. 1A, a conventional lens 10 includes a light incident plane 12, a light exit plane 14 and an optical axis 16. When the white light W is incident to lens 10 parallel to the optical axis 16 via the light incident plane 12 of the lens 10, the white light W is refracted by the lens 10. Then, the white exits the lens 10 via the light exit plane 14. Thereafter, the white light W is refracted into at least three primary color light, such as a blue light B, a green light G and a red light R respectively. Since the wavelengths of the blue light B, the green light G and the red light R are not the same, the intersections of the blue light B, the green light G and the red light R with the optical axis 16 (i.e., the positions b, g, and r shown in FIG. 1A) are not the same. Therefore, the aberration of the white light is generated.
The generation of aberration is proportional to the dispersion of the lens. Accordingly, elimination of generation of aberration is highly desirable. Therefore, specific achromatic lens system or apochromatic lens system for eliminating aberration have been developed. The conventional lens system described above is generally composed of at least two different lenses.
FIG. 1B is a drawing schematically illustrating a conventional lens system for eliminating aberration. Referring to FIG. 1B, a conventional lens system 100 includes a crown glass lens 110 and a flint glass lens 120, wherein the crown glass lens has a lower dispersion than the flint glass lens. The crown glass lens 110 includes a light incident plane 112, light exit plane 114 and an optical axis 116. When the white light W is incident to the lens 110 via the light incident plane 112 parallel to the optical axis 116, after the refraction via the crown glass lens 110 and flint glass lens 120, the intersections of the color light R and B with the optical axis 116 are the same. Therefore, the aberration between the blue light B and the red light R is compensated by the lens system 100.
It is noted that the conventional lens system 100 is composed of at least two different lenses such as lenses 110 and 120, and the compensation effect to the chromatic aberration of the lens system 100 is dependent on the arrangement of these lenses. Therefore, any tiny defect, such as the error in the installation of the lens system 100, the error in the size of the lens, or a shock or crack in the lens system 100 will obviously influence the compensation effect to the chromatic aberration. Therefore, the yield rate of the lens system 100 is low and cost is high.